1. Field of the Invention
The present invention relates to a method for the removal of Mn from cobalt sulfate solutions, and more particularly to a method for removing Mn from the cobalt containing solutions by oxidative precipitation and liquid/solid separation to obtain a purified cobalt containing solution with substantially depleted Mn content.
2. Description of the Prior Art
The demand for valuable metals such as cobalt has increased in many industrial fields. The value of cobalt is very high since highly purified cobalt is difficult to extract from raw materials such as ores. The major source of cobalt comes from lateritic or oxide ores which are accompanied by a variety of different elements such as Ni, Zn, Cu and Mn. Some elements contained in ores have similar chemical properties to cobalt, making their separation rather difficult. One of the impurities which is difficult to separate is Mn. To supply the industrially required purified cobalt, Mn must be removed in a cobalt purification process. One of the cobalt purification methods for removing Mn is dissolving the cobalt containing material in an acidic solution and then chemically treating cobalt and Mn in the solution.
For example, Fonseca et al discloses, in “Proceedings of the international symposium on Electrometallurgical Plant Practice, held at Montreal, Quebec, Canada, Oct. 21–24 in 1990”, a method for the removal of low concentrations of cobalt and Mn from a zinc sulfate solution using sodium hypochlorite (NaOCl). The test results showed that over 99.9% Mn was removed and between 33–99.7% Co was removed from Zn sulfate solution. This process is not effective in an industrial scale process, since the removal of Mn would not be possible without co-precipitating substantial quantities of cobalt and it is difficult to separate Co from the co-precipitated mixture.
Zhang et al discloses, in “Hydrometallurgy vol. 63 pp 127–135 published in 2002”, a method for oxidative precipitation of Mn with SO2 and O2 to separate it from Co and Ni. EP1159461 discloses a method for recovering of Ni and Co from lateritic ore leach liquor, which beside Ni and Co contains a number of impurities such as Mn, Mg and Ca. According to this method, Ni and Co are selectively recovered from this liquor by ion exchange using bis-2-picolyl amine resin, which is highly selective for Ni and Co over the impurity elements.
EP1305455 discloses an apparatus and a method for producing high purity metals such as Co. According to this method, Co is selectively extracted from CoCl2 and/or CoSO4 solution by a combination of electrolysis and ion exchange.
JP2002-241856 discloses a method for recovering valuable metal from used nickel-hydrogen secondary battery by oxidative precipitation. According to that method, valuable metals such as Ni and Co can be recovered from a sulfuric acid solution containing valuable metals by removing Mn using nickelic and/or cobaltic hydroxide as an oxidizing agent.
It is difficult to selectively separate Mn from the co-precipitated material.
So far, none of the known cobalt purification method can remove Mn essentially completely (below 10 ppm level) from cobalt containing solution without co-precipitating substantial quantities of cobalt.
Thus purified cobalt obtained by purifying the cobalt containing solution contains more than 10 ppm of Mn. Therefore, it is desired to develop a method for separating Mn from cobalt containing solution, which enables to obtain cobalt with Mn content of 10 ppm or less.